/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.ipc;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.security.UserGroupInformation;
import org.apache.hadoop.security.SaslRpcServer.AuthMethod;

/**
 * The IPC connection header sent by the client to the server on connection
 * establishment.
 */
// IPC客户端与服务器建立连接时发送的第一条消息
class ConnectionHeader implements Writable {
	public static final Log LOG = LogFactory.getLog(ConnectionHeader.class);

	private String protocol;
	private UserGroupInformation ugi = null;
	private AuthMethod authMethod;

	public ConnectionHeader() {
	}

	/**
	 * Create a new {@link ConnectionHeader} with the given
	 * <code>protocol</code> and {@link UserGroupInformation}.
	 * 
	 * @param protocol
	 *            protocol used for communication between the IPC client and the
	 *            server
	 * @param ugi
	 *            {@link UserGroupInformation} of the client communicating with
	 *            the server
	 */
	public ConnectionHeader(String protocol, UserGroupInformation ugi, AuthMethod authMethod) {
		this.protocol = protocol;
		this.ugi = ugi;
		this.authMethod = authMethod;
	}

	@Override
	public void readFields(DataInput in) throws IOException {
		protocol = Text.readString(in);
		if (protocol.isEmpty()) {
			protocol = null;
		}

		boolean ugiUsernamePresent = in.readBoolean();
		if (ugiUsernamePresent) {
			String username = in.readUTF();
			boolean realUserNamePresent = in.readBoolean();
			if (realUserNamePresent) {
				String realUserName = in.readUTF();
				UserGroupInformation realUserUgi = UserGroupInformation.createRemoteUser(realUserName);
				ugi = UserGroupInformation.createProxyUser(username, realUserUgi);
			} else {
				ugi = UserGroupInformation.createRemoteUser(username);
			}
		} else {
			ugi = null;
		}
	}

	@Override
	public void write(DataOutput out) throws IOException {
		Text.writeString(out, (protocol == null) ? "" : protocol);
		if (ugi != null) {
			if (authMethod == AuthMethod.KERBEROS) {
				// Send effective user for Kerberos auth
				out.writeBoolean(true);
				out.writeUTF(ugi.getUserName());
				out.writeBoolean(false);
			} else if (authMethod == AuthMethod.DIGEST) {
				// Don't send user for token auth
				out.writeBoolean(false);
			} else {
				// Send both effective user and real user for simple auth
				out.writeBoolean(true);
				out.writeUTF(ugi.getUserName());
				if (ugi.getRealUser() != null) {
					out.writeBoolean(true);
					out.writeUTF(ugi.getRealUser().getUserName());
				} else {
					out.writeBoolean(false);
				}
			}
		} else {
			out.writeBoolean(false);
		}
	}

	public String getProtocol() {
		return protocol;
	}

	public UserGroupInformation getUgi() {
		return ugi;
	}

	public String toString() {
		return protocol + "-" + ugi;
	}
}
